What’s the point in penetrating the labyrinthine hearts of some the world’s highest glaciers? For one thing, to monitor water conduction and storage inside glacial ice, the largest untapped and uncontaminated reserve of fresh water left on the planet. The rush to study this “blue gold”—and forestall glacial retreat—has assumed an even greater urgency as the world’s aquifers and rivers have begun to run dry.

“We know that glaciers store enormous amounts of water,” Badino says, “but we don’t know a lot about how or where. Direct observation from scuba diving may give us some answers.” Badino’s quest to find these answers has taken him to Iceland, Argentina, Chile, and with greatest frequency, to Switzerland’s Gorner Glacier, the most cave-riddled—or “karstic”—slab of ice in the Alps. Upending conventional scientific wisdom, however, comes with a price: Badino has found only five people willing to attempt glacial cave diving with him; few colleagues want to risk their lives working under millions of tons of shifting ice. “When you are on the cutting edge,” he says wistfully, “you are always alone.”

Such are the occupational hazards of professional peregrine “salvage,” an ongoing effort to protect the offspring of one of America’s most threatened species. After more than 30 years on the brink of extinction, F. peregrinus anatum now seems to be not only surviving amidst humanity, but thriving—as growing numbers nest on man-made structures such as radio towers, bridges, and high-rise buildings. The falcon’s comeback would be a happy ending, except for the fact that 30 to 50 percent of chicks in urban nests are swept to their deaths by erratic crosswinds as they make their first attempts at flight.

To prevent this, Latta transports the chicks from high-mortality nests to captive breeding facilities across the state, where adult falcons care for the adoptees until they are old enough to fledge. Later, he releases the young peregrines at natural nesting sites in cliffs along the coast.

No surprise: Latta, 39, has become an expert climber. He logs dozens of hours a year strapped into a harness, inching up ventilation shafts to capture chicks and then dodging small rockslides as he “translocates” them to the wild. “I still get this ball of nausea beforehand,” he says. “But if you’re not scared, you’re just stupid.”

Carnivorous, cold-blooded, and primarily nocturnal, the black caiman is the largest predator in the Amazon and the largest crocodilian in the Western Hemisphere. It can weigh more than 600 pounds, live for a century, and is one of only a dozen or so species capable of preying on humans. And, thanks to a once-lucrative international skin trade, it’s also endangered; until recently, little was known about its life in the wild.

All of which explains why Da Silveira motors out onto Lake Mamirauá at 1 a.m. in his wooden skiff, hoping to catch the toothy reptile. When he spots one, he glides to within an arm’s reach, uses a bamboo pole to slip a noose around its neck, ties its jaws shut with string (“They can swing their heads like clubs,” he says, “and break your shins in half”), binds its legs, and starts taking measurements: weight, length, girth, and age. Then he releases the beast—carefully.

Despite 3,000 captures over 11 years, Da Silveira has suffered no injuries. “But my assistants are terrified,” he says.”They think I’m trying to capture the devil.”

For volcanologist Hugo Delgado Granados, the top of Mexico is where the research starts getting good. At 42, he has spent the better part of 20 years collecting data on the country’s three highest volcanoes—Pico, 17,343-foot Iztaccíhuatl, and 17,887-foot Popocatépetl—a mission he describes as equal parts science and humanitarianism. Popo is located just 45 miles southeast of Mexico City and, in the event of a massive eruption, could blanket more than 400,000 people with deadly mudflows and pyroclastic avalanches of gas and debris. Since its last eruption in December 1994, Popo’s crater has been boiling with magma, and the summit glacier has been shrinking by the day.

With any luck, Delgado’s research will eventually insure that if “the big one” hits, no one will be in the way. When he can enlist a willing pilot, he helicopters onto the ash-strewn rims or flies planes through smoke plumes to measure temperatures and gather gas samples; on foot, he rappels 400 feet into craters and crevasses. In two decades of work, he’s been rocked by seismic shock waves, temporarily blinded by ashfall, and choked by sulfurous smoke.

So when will Popo blow? Delgado shakes his head. “All the data tell us for sure is that Popo has much more to say.”

Peter Lane Taylor’s first book, Science at the Extreme, will be published this month by McGraw-Hill.